1. Field of the Invention
This invention relates to power supplies, and more particularly relates to integrating two or more power supplies to work together to provide increased efficiency to a load at high and low power levels.
2. Description of the Related Art
A power supply, sometimes known as a power supply unit or PSU, is a device or system that supplies electrical or other types of energy to an output load or group of loads. A power supply, in some embodiments may be configured to convert power in one form to another form, such as converting alternating current (“AC”) power to direct current (“DC”) power. The regulation of power supplies is typically accomplished by incorporating circuitry to tightly control the output voltage or current of the power supply to a specific value or very small range of specific values. The specific value is closely maintained despite variations in the load presented to the power supply's output, or any reasonable voltage variation at the power supply's input.
For example, in an electrical device such as a computer, the power supply is typically designed to convert an AC voltage input, such as is traditionally provided by a conventional wall socket, into several low-voltage DC power outputs for transmission to the internal components of the computer. Conversion is sometimes performed in stages that may include different power supply topologies such as a rectification stage, a boost stage, buck stage, or other topology.
Circuitry typically associated with power supplies relies on switching elements which are turned on and off at a fixed switching rate to maintain the output voltage. For example, if a switching rate is 100 kilo-Hertz (“kHz”), the switching period is 10 micro seconds. Duty cycle is typically a ratio of an amount of time a switch is commanded on during a switching period divided by the switching period. If a switch is commanded on for 5 microseconds of a 10 microsecond switching period, the duty cycle is 5 microseconds divided by 10 microseconds or 0.5. The minimum duty cycle is 0 and the maximum duty cycle is 1.0.
Power supplies cannot convert all of the energy drawn from a source to another form without some dissipation of energy within the power supply. Typically components within the power supply dissipate some heat due to parasitic resistance, inductance, and capacitance. Efficiency is a measure of energy dissipation within a power supply and is typically expressed as a ratio of power supplied to a load from the power supply divided by input power received by the power supply. Often efficiency is not uniform across an entire range of power that can be provided by a power supply. Typically, efficiency of a power supply drops as the power supply becomes lightly loaded. Often this is due to switching losses in switching elements within a power supply.
Low efficiency is undesirable because energy is wasted and power dissipated in a power supply is usually transformed to heat that can damage components and requires cooling. In order to improve efficiency of power supplies, and thus reduce wasted energy, the Environmental Protection Agency (“EPA”) is in the process of implementing standards that will require all power supplies to meet at least 80% efficiency when operating at 20%, 50%, and 100% of full load capacity of a power supply. The conventional art does not address this problem or provide a means whereby the power supplies can operate efficiently enough to meet EPA standards.